The present invention has applicability to power tools, and in particular to power tools having reciprocating drive mechanisms. Jigsaws and other reciprocating saws (referred to in the trade as "recipro" saws) are the most common types of power tools having a reciprocating drive mechanism. However, it will be understood that the present invention has general applicability to any power tool that utilizes a reciprocating drive mechanism.
Reciprocating saws of the general type to which the present invention pertains typically comprise an electric motor arranged to drive a reciprocating saw blade drive mechanism, which may be of the scotch yoke type. More particularly, the motor shaft is mechanically coupled to a crank plate having an eccentrically located crank pin that is drivingly received within the slot of a reciprocating yoke member. The yoke member is coupled to the saw blade plunger sometimes referred to as a ram.
Mechanisms of the type described, although generally satisfactory, do not provide a means for adjusting the stroke of the reciprocating member. As is known to those skilled in the art, it is desirable to be able to vary the stroke of a reciprocating saw blade depending on the nature of the work being cut.
Reciprocating saws and jigsaws are used to cut a variety of materials, including materials which differ widely in density. As is known to those skilled in the art, as a general rule it is desirable when cutting soft materials to provide the saw blade with a rather large stroke, say two inches for purposes of illustration. On the other hand, when cutting hard materials it is desirable to provide the blade with a much shorter stroke, say a stroke of one inch for purposes of illustration. Thus, it is very desirable to provide an adjustable stroke reciprocating mechanism thereby to permit the tool to cut efficiently irrespective of the nature of the material being cut.
Aside from varying the stroke of the saw blade to accommodate materials of varying properties, it is also advantageous to be able to shorten the stroke of the saw blade to be able to cut objects in cramped or confined environments. Minimizing the stroke of the blade in such an instance reduces the possibility of unintended contact between the tip of the blade and other objects in the vicinity of the member being cut.
Power tools of the type under consideration are provided with foot plates which engage the work being cut and which permit the operator to position the power tool relative to the work being cut. As is known to those skilled in the art, there is an optimum position for the foot plate for a given stroke of reciprocation. Consequently, it is desirable to adjust the foot plate automatically upon adjustment of the stroke of reciprocation such that the foot plate will be properly positioned for the selected stroke of reciprocation.